Recently, electric devices such as motors have become widespread, a possibility of an abnormal operation of the electric device leading to a serious accident is further increased. Thus, it is required to reduce a risk of an accident as much as possible. To put the risk occurrence within an allowable limit, international standards have been established. In one example, IEC61508 is defined as a standard for the electric device. IEC61800-5-2 is specified as a standard of a driver such as a motor.
When a safety signal is input, an inverter must not deliver power to the motor as defined in IEC 61800-5-2.
FIG. 1 shows a configuration of a conventional inverter-protecting device.
An inverter 100 receives AC power of three phases. Then, a rectifying module 101 in the inverter 100 rectifies the AC power. Then, a smoothing module 102 therein smoothes and stores a DC voltage rectified by the rectifying module 101. An inverting module 103 therein receives the DC voltage stored in a DC link capacitor as the smoothing module 102, and converts the DC voltage into an AC voltage having a predetermined voltage and frequency according to a PWM control signal, and, outputs the converted AC voltage to a motor 200. The inverting module 103 is configured to have three-phase legs. Each leg includes two switching elements connected in series. The switching element of the inverting module 103 is, for example, an insulated gate bipolar transistor (IGBT).
A safety relay 130 receives 24 V from the inverter 1. The safety relay 130 includes first and second switches 131 and 132 connected in parallel. The safety relay 130 has a closed state as a normal operation state.
When 24V is input to a SA terminal via the first switch 131, a first insulating module 140 insulates the corresponding voltage signal. A first receiving module 150 outputs a voltage detection signal. The first receiving module 150 is, for example, a photo coupler. The first receiving module 150 outputs a high-level voltage detection signal when an input voltage thereto is equal to or greater than a predetermined threshold, while the first receiving module 150 outputs a low-level voltage detection signal when the input voltage thereto is smaller than the predetermined threshold.
When 24V is input to a SB terminal via the second switch 132, a second insulating module 145 insulates the corresponding voltage signal. A second receiving module 155 outputs a voltage detection signal. The second receiving module 155 is a photo coupler. The second receiving module 155 outputs a high-level voltage detection signal when an input voltage thereto is equal to or greater than a predetermined threshold, while the second receiving module 155 outputs a low-level voltage detection signal when the input voltage thereto is smaller than the predetermined threshold. A transistor 160 prevents overcurrent and maintains a constant voltage.
When the first receiving module 150 outputs the high-level voltage detection signal, a controller 110 provides a pulse width modulation (PWM) control signal to a gate block 120. The gate block 120 outputs the PWM control signal to the inverting module 103 of the inverter 1. When the second receiving module 155 outputs the high-level voltage detection signal, the controller allows an enable pin of the gate block 120 to be active to enable the PWM control signal provided from the controller 110 to be outputted to the inverting module 103.
When the first receiving module 150 outputs the low-level voltage detection signal, this signal is input to a trip zone of the controller 110. The controller 110 prevents the PWM control signal from being provided to the gate block 120. Further, when the second receiving module 155 outputs the low-level voltage detection signal, the controller allows a disable pin of the gate block 120 to be active so that the PWM control signal is not output to the inverting module 103.
That is, when at least one of the first receiving module 150 and the second receiving module 155 outputs the low-level voltage detection signal, the PWM control signal may be prevented from being supplied to the inverting module 103. Thus, the electric power may be prevented from being supplied to the motor 200.
In such a conventional protection device, it is necessary for software to verify that the trip zone of the control unit 110 operates normally. Thus, there occurs a problem that such verification takes time and cost.